Atari 2600 NTSC simple DIY Composite mod

[gtremblay]

juste a follow up for the NTSC composite mod on Atari 2600 JR.

 

 

The TIA chip differs between PAL and NTSC.

most mods I've seen are for PAL.

like : https://www.console-corner.de/videomod.html

(PAL_MOD_SPOT.JPG attached)

TC4050 PIN 2 - 3K3 Widerstand
TC4050 PIN 10 - 2K2 Widerstand
TC4050 PIN 12 - 330 Widerstand
TC4050 PIN 15 - 1K  Widerstand
TIA PIN 9 Color - 1K Widerstand & 100p Kondensator
Audio
 

 

Which give weird color with NTSC machine.

 

so the instead using pins 5-6-7 of TIA PAL for LUM0, LUM1 and LUM2

 

 

I use the 5-7-8 pins with TIA NTSC

 

so at the end:

sync for both PAL and NTSC is  pin 12 (CD4050)    = TIA 2

lum1 for both PAL and NTSC is pin 10  (CD4050)   =  TIA 5

 

then :

FOR PAL

 

lum2 pin 15  (CD4050)    =  TIA 6
lum0 pin 2    (CD4050)    = TIA 7

 

FOR NTSC

lum2  from pin 15 (for PAL) to  pin2 (for NTSC) (CD4050)    =  TIA 7
lum0  from pin 2 (for PAL) to  pin 6 (for NTSC)  (CD4050)    =  TIA 8

 

 

if you do PAL mod on NTSC machine, black background will appear grey and you'll have some weird color like (PAL mod on NTSC machine picture)

in ICE hockey, the ice is grey instead of white and so on...

 

 

 

 

 

[Voxel]

On 7/12/2020 at 7:53 PM, gtremblay said:

 

Nice work.

 

Surprised you did not park up your car when you used your phone to take a picture of your day out, would have been a lot clearer.

[gtremblay]

thanks!

 

yeah.. now you say it, I realize that I should stop my car (and not just drop the joystick ) before taking the pictures..

 

I was just too focused on the background colors...

 

[Voxel]

We all get caught up admiring our good work.

[Shawn]

nm, answered my own question with a second read.

 

 

 

Edited December 27, 2020 by Shawn

[Shawn]

So this attached diagram would be for PAL or NTSC installation? I'm looking for a proper diagram for NTSC installation please.

 

Edited December 27, 2020 by Shawn

[gtremblay]

Maybe I'm too late and you figure it out but your diagram is for PAL, pin 15 is not use in NTSC version

the difference for NTSC is :

instead of pin 15 (for PAL) , it is pin2 (for NTSC)
instead of pin 2 (for PAL) , it is pin 6 (for NTSC)

 

[Daddelretro]

I did this mod on my NTSC Junior console, but I have a strong ghosting:

If I switch to B/W, the ghosting disappears:

 

Can anyone point me to a solution for this?

 

[Level42]

Has anyone ever explained why a CD4050 is used ? I've seen simple mods with just a single transistor, what's the difference between using a CMOS non-inverting Hex buffer and a simple transistor and why not use a TTL non inverting hex-buffer, CMOS are know to be relatively slow.

 

Just wondering :)

[+batari]

On 8/12/2022 at 7:03 AM, Level42 said:

Has anyone ever explained why a CD4050 is used ? I've seen simple mods with just a single transistor, what's the difference between using a CMOS non-inverting Hex buffer and a simple transistor and why not use a TTL non inverting hex-buffer, CMOS are know to be relatively slow.

 

Just wondering :)

Surprisingly there is actually no non-inverting hex TTL buffer with normal outputs with a remotely similar ubiquity as the CD4050. There are only rare/obscure examples and many with alternate outputs (like open collector or Schmitt trigger).

 

Besides, the 2600’s dot clock is only 3.57 MHz which the CD4050 can handle. 
 

Really, though, I don’t know that this circuit is ideal without a transistor. The output comes directly from the resistor ladder and so the impedance is certainly far from correct.  

[Level42]

Ah surprised ab out the TTL info.... LOL.

 

Yeah well I have a Sunnyvale (NTSC of course) 4 switcher here (in PAL land) with a CD4050 mod and I hadn't used it for quite some time and hooked it up again recently and where it worked fine before, I do get a working picture except it doesn't sync.

I may have tried it on another TV before though, so maybe one is less "picky" about the sync then the other.... will have to try that other TV....

Edited August 15, 2022 by Level42